Hormones separable from frog pituitary by PAGE appear to control growth of the lens epithelium. In hypophysectomized animals mitosis and DNA synthesis are absent 3 to 4 weeks postoperatively. The phenonenon has thus far proved to be specific for the anuran lens. Growth is reinitiated by administration of frog prolactin and growth hormone. We will endeavor to show: (1) whether or not the hormones isolated cross react, (2) to which cells in the pars distalis they are localized, (3) to what mitogen they give rise, and (4) where this mitogen is synthesized. In addition, the correlation between lens fiber growth and mitosis will be characterized further. We shall assess the validity of the earlier hypothesis we have made relative to the genesis of radiation cataract. Frog lens epithelial culturing technique will be improved in attempts to study the mode of mitogen action.